Since after birth the supply of nutrients to the body is maintained by intestinal absorption, derangements of gastrointestinal function could adversely affect proper growth and development of the infant and child. Information regarding growth and function of gastrointestinal tract under normal and unusual conditions is lacking or scanty during infancy and childhood. The purpose of this research is to study in animal models the maturation of the intestinal tract under normal and unusual conditions. The developmental characteristics of small intestinal absorption of monosaccharides (glucose, galactose), disaccharides (lactose, sucrose and maltose), amino acids (glycine, lysine and valine) and minerals (calcium and magnesium) will be measured in 7 to 8, 14 to 15, 21 to 23, 28 to 31 and 70 to 73 day old rats. Intestinal absorption will be assessed by an in situ perfusion of the whole small intestine and its segments as described in the original grant. This supplemental grant is mainly for salaries, and supplies. The salaries are for the principle investigator and technicians, and supplies are mainly for purchase of rats and radioactive substances, the justifications are given in the section on buget.